This invention relates to a process for cooling a gaseous stream before and/or during compression by introducing a liquid which evaporates at least partially in the gaseous stream, as well as to an apparatus for performing the process.
It is known from the prior art that the heat of compression produced during the compression of a stream of gas can be removed by injecting a condensate of this gas into the compressor. In the compressor, the condensate evaporates by removing heat from the gaseous stream to be compressed. This process is utilized for the compression of steam by using water as the injected cooling liquid. Another such process is disclosed in Offenlegungsschrift No. 28 01 408 wherein a cooling fluid injected into a compressor is cooled by injection of a liquid. The liquid consists of a mixture of oil and a liquified portion of the cooling fluid. Cooling of the gaseous stream to be compressed is effected by evaporation of the liquified cooling fluid, whereas the oil is utilized for lubrication and sealing of the compressor.
In these prior art processes, it has been a requirement that the condensate injected as the cooling liquid must have essentially the same composition as the gaseous stream to be cooled. This is because the gas would be contaminated if the evaporating liquid had another composition. However, this is an undesirable restriction. In addition, an optimum cooling may not be possible when using a condensate that has the same composition as the gaseous stream to be compressed, depending on the pressure and temperature of the gas to be compressed during compression. On the other hand, if injection of a liquid of another composition were possible, this would bring optimum results because a liquid having a high heat of evaporation, with respect to the gas to be cooled, can be chosen. Moreover, if the boiling points of the main components of the gas and the liquid could be chosen to differ considerably, and as a result the partial pressure of the evaporating liquid is substantially reduced, this results in a Joule-Thomson cooling effect.